VOL.
XXIX
NO.
2
THE
COMPARATIVE
IN
JOURNAL
VITRO
OF
ANTIBIOTICS
ACTIVITY
DOROTHY STEWART and
OF
181
CEPHALOSPORINS
GERALD P. BODEY
Department of Developmental Therapeutics, The University of Texas System Cancer Center, M. D. Anderson Hospital and Tumor Institute at Houston, Houston, Texas 77025, U. S. A. (Received The
in
vitro
activity
of
for publication cephalexin,
September
16, 1975)
cephaloridine,
cephalothin,
cephapirin,
cefoxitin, cephamycin C, cephradine, cephacetrile and cefazolin was determined against 443 isolates of bacteria. At a concentration of 12.5 µg/ml, all of the cephaIosporins inhibited more than 60 % of the isolates of Klebsiella pneumoniae. At the same concentration, cephalexin, cephaloridine, cephalothin, cephapirin, cefazolin inhibited more than 90 % of isolates of Proteus mirabilis. losporins except cephalothin and Escherichia coli at a concentration cephalosporin against gram-negative activity of cephalosporins against active cephalosporin against these
cephamycin C and All of the cepha-
cephapirin inhibited over 60 % of isolates of of 12.5 µg/ml. Cefoxitin was the most active bacilli. There were substantial differences in the gram-positive organisms.
cocci. Cephaloridine There was considerable
was the most fluctuation in
the proportion of isolates of gram-negative bacilli susceptible to these cephalosporins from year to year, but there was no evidence to suggest that the number of resistant isolates was increasing.
Gram-negative bacilli are a common cause of infections in hospitalized cancer patients. Consequently, the discovery of new antibiotics with activity against these organisms are of major importance. Cephalosporins have proven to be significantly active against Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis and most gram-positive cocci.1) Since the introduction of cephalothin, numerous derivatives have been synthesized which offer advantages such as oral administration, less toxicity and higher and more prolonged serum concentrations. This study was initiated to evaluate the comparative in vitro activity of the cephalosporins against gram-negative bacilli and gram-positive cocci and to determine whether the increased use of these antibiotics had resulted in the emergence of increasing numbers of resistant organisms. Materials and Methods Susceptible testing was conducted on 443 isolates of gram-negative bacilli and gram-positive cocci using a dilution technique with an automatic microtiter system.2.3) The organisms were inoculated into MUELLER-HINTON broth (Difco) and incubated at 37°C for 18 hours. A 0.05-ml sample of 10-3 dilution of the broth cultures of gram-negative bacilli and Staphylococcusaureus (approximately 106 colony forming units/ml) was used as the inoculum for the susceptibility tests. A 0.05-ml sample of a 10-2 dilution of the broth cultures of Diplococcus pneumoniae and Streptococcus pyogenes (approximately 106 colony forming units/ml) was used as the inoculum. All gram-negative bacilli were isolated from blood specimens of patients between 1967 and 1973. The majority of these patients were hospitalized at this institution and had underlying malignancies. A total of 160 isolates of K. pneumoniae, 130 isolates of E. coli and 88 isolates of P. mirabilis were tested. Supported Health,
in part
U. S. Public
by
Grant
Health
CA Service,
10042 from Bethesda,
the
National
Maryland
Cancer 20014.
Institute,
National
Institutes
of
THE
182
JOURNAL
OF
ANTIBIOTICS
FEB.
1976
All gram-positive cocci were obtained from hospitalized patients, some of whom did not have cancer. A total of 15 isolates of Diplococcus pneumoniae and 50 isolates of Staphylococcus aureus were studied. Isolates of S. aureus were tested according to their susceptibility to penicillin G. Those 25 organisms inhibited by less than 0.10 µg/ml were considered to be penicillin G susceptible and those 25 organisms resistant to more than 25µg/ml were considered to be penicillin G resistant. µg The antibiotics, cephalothin, cephalexin and cephaloridine were supplied by Eli Lilly and Co., Indianapolis, Indiana. Merck, Sharp & Dohme supplied cephamycin C and cefoxitin. Cephradine, cephapirin, cefazolin and cephacetrile were obtained from the following companies, respectively: E. R. Squibb & Sons, Inc., Princeton, N. Y.; Bristol Laboratories, Syracuse, New York; Smith Kline & French, Philadelphia, Penn. and CIBA Pharmaceutical Co., Summit, N.J. Initial concentrations of 1,000µg/ml were prepared and appropriate dilutions from this stock concentration were made. Fig. 1. Activity of cephalosporins cherichia coli (130 isolates tested).
Results
At a concentration the
cephalosporins
cephapirin
of
12.5 µg/ml,
except
inhibited
over
At
only
the same
losporins
6%
inhibited
of K. pneumoniae 90%,
but
Cefoxitin,
(Fig. 3). cephalexin,
Fig.
2.
the
inhibited
isolates inhibited
only
and cefazolin
cephalosporins
Activity spp.
of
Cefoxitin
against
Cephalexin Cephaloridine Cephalothin Cephapirin Cefoxitin Cephamycin C Cephradine Cephacetrile Cefazolin
65%.
were
the
P. mirabilis
At a concentration of 12.5 µg/ml, cephaloridine, cephalothin, cepha-
cephamycin
siella
respectively.
all of the cepha-
over 60%
cephapirin
of
and cephalothin
38 %,
(Fig. 2).
cephalothin
most active
pirin,
and
concentration,
Es-
and
60 % of the isolates
of E. coli (Fig. 1). Cephapirin inhibited
all
cephalothin
against
C and
cefazolin
of cephalosporins
(160 isolates Cephalexin Cephaloridine Cephalothin Cephapirin Celoxitin Cephamycin C Cephradine Cephacetrile Cefazolin
tested).
inhibited
against
Kleb-
Fig. 3. Activity of cephalosporins mirabilis (88 isolates tested). Cepholexin Cephaloridine Cephalothin Cephapirin Cefoxitin Cephamycin C Cephradine Cephacetrile Cefazolin
against Proteus
VOL.
XXIX Fig.
NO.
2
4.
THE
Activity
JOURNAL
of cephalosporins
against
OF
183
ANTIBIOTICS
penicillin
G resistant
Staphylococcus
o-o-
Fig.
5.
Activity
of cephalosporins
against
penicillin
Cepholexin Cephaloridine Cephalolhin
~-
Cephopirin
o-•-•-
Cefoxitin Cephomycin Cephrodine Cephocetrile
o--
Cefozolin
G sensitive
aureus.
C
Staphylococcus
aureus.
Cephalexin Cephaloridine Cephalothin Cephapirin Cefoxitin Cephamycin C Cephradine Cephacetrile Cefazolin
more
than
90 % of these isolates.
Cefoxitin inhibited
was consistently
87 % of isolates
6.25 µg/ml, There
it inhibited were
intermediate mycin
cephalosporin
differences
of
of K. pneumoniae in the
against
in vitro
and cefoxitin, against
both
cephalexin
penicillin
gram-negative
12.5µg/ml. and
activity
and resistant S. aureus (Figs. 4 and 5). of S. aureus. Cephalothin, cefazolin,
in activity,
C was inactive
active
of E. coli at a concentration
84 % of isolates
substantial
penicillin G sensitive against both groups
the most
At
the
and resistant
It of
of P. mirabilis.
cephalosporins
Cephaloridine cephacetrile
and cephradine
G sensitive
a concentration
100 % of isolates of
bacilli.
against
was the most active and cephapirin were
were
least active.
S. aureus.
There
Cephawere
VOL.
XXIX
inhibited
from
THE
1 lists the proportion
cephalosporin
substantially during
2
JOURNAL
only 47 % at a concentration
Table of each
NO.
by year.
from year to year.
this period.
to 92 j.
Some
in susceptibility statistically
of
significant
of E. coli and
The susceptibility Cephalothin
of these
of isolates
are statistically
Likewise,
the
bacilli
most extensively
significant. and
differences cephapirin
to 12.5 µg/ml has fluctuated
at this institution
to this antibiotic
K. pneumoniae
in 1968
pneumoniae to cephalothin, cephalexin, cephaloridine, to 1968 are statistically significant (p=.001~.007).
sensitive
gram-negative
of E. coli susceptible
of susceptible
of E. coli to cephalothin
(p=.003).
185
K. pneumoniae
has been used
the proportion
these differences
of isolates
ANTIBIOTICS
of 6.25 µg/ml.
of isolates
The proportion
16 % to 64 % whereas
OF
For example, 1973
has varied
has varied
and cefazolin
44%
the differences
compared
in susceptibility
from
to
1971 are
of isolates
of K.
in 1970 compared
Discussion This in vitro data indicates that the cephalosporin antibiotics have a broad spectrum of activity against gram-negative bacilli and gram-positive cocci. Cefoxitin was the most active antibiotic against isolates of gram-negative bacilli. WALLICK and HENDLIN found similar results with their susceptibility testing of cefoxitin.4) Cefazolin inhibited 78 % of the Klebsiella spp. isolates at a concentration of 6.25 µg/ml. TURCK et al. found similar results with cefazolin. In their study, more than 80% of isolates were inhibited by a concentration of 5 µg/ml or less.5) Cephapirin exhibited the least activity against isolates of E. coli and Klebsiella spp. whereas cephradine was least active against P. mirabilis. S. aureus isolates were most sensitive to cephaloridine and cephalothin, and the results were similar regardless of their susceptibility to penicillin G. Other investigators found that cefazolin was equally active against penicillin G sensitive and resistant S. aureus.5) However, in this study, cefazolin was less active against penicillin G resistant isolates of S. aureus. At a concentration of 0.20µg/ml, cefazolin inhibited 68 % of penicillin G sensitive isolates, but only 24% of penicillin G resistant isolates. Cefoxitin, cephalexin and cephradine were the least active cephalosporins against gram-positive cocci, except for cephamycin C which was inactive against S. aureus and only marginally active against D. pneumoniae. In NEU'S study, cefoxitin had similar activity as cephalexin.6) In the study of BERGERON et al., cefazolin and cephaloridine were more active than cephalothin and cephalexin against D. pneumoniae.7) However, cephaloridine is not as consistently active as cephalothin when a high inoculum of S. aureus is used. The susceptibility of isolates of E. coli and K. pneumoniae to the cephalosporins has fluctuated substantially during the years from 1968 to 1973. Some of the most striking differences were observed with isolates of K. pneumoniae, comparing 1968 with 1970, differences which were statistically significant. It was not possible to correlate the dramatic decrease in cephalosporin susceptibility in 1970 to any change in antibiotic usage in this institution. Fortunately, since that time, the number of cephalosporin resistant isolates has decreased, although cephalothin usage was not altered. An explanation for this fluctuation in susceptibility is not readily apparent. Cefoxitin susceptibility fluctuated the least and it was the most active of the cephalosporins. This cephalosporin is resistant to hydrolysis by gram-negative bacilli. Some of the variability in the sensitivity of E. coli to cephalosporins may be due to the fact that E. coli vary in their ability to produce ß-lactamases which results in their resistance. Another factor which may play a role is the degree of cell permeability to the antibiotics. Although K. pneumoniae seldom produce cephalosporinases, it is possible that the production of cephalosporinases may explain the changing susceptibility of these organisms to cephalothin.1)' In vitro evaluation of the cephalosporins has indicated that they have substantial differences in activity against gram-positive cocci and gram-negative bacilli. Consequently, use of a single
VOL.
XXIX
inhibited
from
THE
1 lists the proportion
cephalosporin
substantially during
2
JOURNAL
only 47 % at a concentration
Table of each
NO.
by year.
from year to year.
this period.
to 92 j.
Some
in susceptibility statistically
of
significant
of E. coli and
The susceptibility Cephalothin
of these
of isolates
are statistically
Likewise,
the
bacilli
most extensively
significant. and
differences cephapirin
to 12.5 µg/ml has fluctuated
at this institution
to this antibiotic
K. pneumoniae
in 1968
pneumoniae to cephalothin, cephalexin, cephaloridine, to 1968 are statistically significant (p=.001~.007).
sensitive
gram-negative
of E. coli susceptible
of susceptible
of E. coli to cephalothin
(p=.003).
185
K. pneumoniae
has been used
the proportion
these differences
of isolates
ANTIBIOTICS
of 6.25 µg/ml.
of isolates
The proportion
16 % to 64 % whereas
OF
For example, 1973
has varied
has varied
and cefazolin
44%
the differences
compared
in susceptibility
from
to
1971 are
of isolates
of K.
in 1970 compared
Discussion This in vitro data indicates that the cephalosporin antibiotics have a broad spectrum of activity against gram-negative bacilli and gram-positive cocci. Cefoxitin was the most active antibiotic against isolates of gram-negative bacilli. WALLICK and HENDLIN found similar results with their susceptibility testing of cefoxitin.4) Cefazolin inhibited 78 % of the Klebsiella spp. isolates at a concentration of 6.25 µg/ml. TURCK et al. found similar results with cefazolin. In their study, more than 80% of isolates were inhibited by a concentration of 5 µg/ml or less.5) Cephapirin exhibited the least activity against isolates of E. coli and Klebsiella spp. whereas cephradine was least active against P. mirabilis. S. aureus isolates were most sensitive to cephaloridine and cephalothin, and the results were similar regardless of their susceptibility to penicillin G. Other investigators found that cefazolin was equally active against penicillin G sensitive and resistant S. aureus.5) However, in this study, cefazolin was less active against penicillin G resistant isolates of S. aureus. At a concentration of 0.20µg/ml, cefazolin inhibited 68 % of penicillin G sensitive isolates, but only 24% of penicillin G resistant isolates. Cefoxitin, cephalexin and cephradine were the least active cephalosporins against gram-positive cocci, except for cephamycin C which was inactive against S. aureus and only marginally active against D. pneumoniae. In NEU'S study, cefoxitin had similar activity as cephalexin.6) In the study of BERGERON et al., cefazolin and cephaloridine were more active than cephalothin and cephalexin against D. pneumoniae.7) However, cephaloridine is not as consistently active as cephalothin when a high inoculum of S. aureus is used. The susceptibility of isolates of E. coli and K. pneumoniae to the cephalosporins has fluctuated substantially during the years from 1968 to 1973. Some of the most striking differences were observed with isolates of K. pneumoniae, comparing 1968 with 1970, differences which were statistically significant. It was not possible to correlate the dramatic decrease in cephalosporin susceptibility in 1970 to any change in antibiotic usage in this institution. Fortunately, since that time, the number of cephalosporin resistant isolates has decreased, although cephalothin usage was not altered. An explanation for this fluctuation in susceptibility is not readily apparent. Cefoxitin susceptibility fluctuated the least and it was the most active of the cephalosporins. This cephalosporin is resistant to hydrolysis by gram-negative bacilli. Some of the variability in the sensitivity of E. coli to cephalosporins may be due to the fact that E. coli vary in their ability to produce ß-lactamases which results in their resistance. Another factor which may play a role is the degree of cell permeability to the antibiotics. Although K. pneumoniae seldom produce cephalosporinases, it is possible that the production of cephalosporinases may explain the changing susceptibility of these organisms to cephalothin.1)' In vitro evaluation of the cephalosporins has indicated that they have substantial differences in activity against gram-positive cocci and gram-negative bacilli. Consequently, use of a single
186
THE
JOURNAL
cephalosporin for routine in vitro susceptibility tion of the appropriate cephalosporin as therapy
OF
ANTIBIOTICS
FEB.
1976
testing is probably inadequate. However, selecalso depends on other factors such as their relative
potential for causing thrombophlebitis and nephrotoxicity and which may offer the advantage of higher serum concentrations
their pharmacological disposition or better tissue penetration.
References
1) HEWITT, W.L.: Cephalosporins-1973. J. Infect. Dis. 128 Supplement, October 1973 2) Canalco: Autotiter IV Instruction Manual 3) STEWART, D. & G.P. BODEY: In vitro activity of sisomicin, an aminoglycoside antibiotic against clinical isolates. J. Antibiotics 28: 149~155, 1975 4) WALLICK, H. & D. HENDLIN: Cefoxitin, a semisynthetic cephamycin antibiotic: Susceptibility studies. Antimicr. Agents & Chemoth. 5: 25~32, 1974 5) TURCK, M.; R. A. CLARK, H. W. BEATY, K. K. HOLMES, W. W. KARNEY & L. B. RELLER: Cefazolin in the treatment of bacterial pneumonia. J. Infect. Dis. 128: S382~385, 1973 6) NEU, H. C.: Cefoxitin, a semisynthetic cephamycin antibiotic: Antibacterial spectrum and resistance to hydrolysis by gram-negative beta-lactamases. Antimicr. Agents & Chemoth. 6: 170~176, 1974 7) BERGERON, M. C.; J. L. BRUSCH, M. BARZA & L. WEINSTEIN: Bactericidal activity and pharmacology of cefazolin. Antimicr. Agents & Chemoth. 4: 396~401, 1973
XXIX
NO.
2
THE
COMPARATIVE
IN
JOURNAL
VITRO
OF
ANTIBIOTICS
ACTIVITY
DOROTHY STEWART and
OF
181
CEPHALOSPORINS
GERALD P. BODEY
Department of Developmental Therapeutics, The University of Texas System Cancer Center, M. D. Anderson Hospital and Tumor Institute at Houston, Houston, Texas 77025, U. S. A. (Received The
in
vitro
activity
of
for publication cephalexin,
September
16, 1975)
cephaloridine,
cephalothin,
cephapirin,
cefoxitin, cephamycin C, cephradine, cephacetrile and cefazolin was determined against 443 isolates of bacteria. At a concentration of 12.5 µg/ml, all of the cephaIosporins inhibited more than 60 % of the isolates of Klebsiella pneumoniae. At the same concentration, cephalexin, cephaloridine, cephalothin, cephapirin, cefazolin inhibited more than 90 % of isolates of Proteus mirabilis. losporins except cephalothin and Escherichia coli at a concentration cephalosporin against gram-negative activity of cephalosporins against active cephalosporin against these
cephamycin C and All of the cepha-
cephapirin inhibited over 60 % of isolates of of 12.5 µg/ml. Cefoxitin was the most active bacilli. There were substantial differences in the gram-positive organisms.
cocci. Cephaloridine There was considerable
was the most fluctuation in
the proportion of isolates of gram-negative bacilli susceptible to these cephalosporins from year to year, but there was no evidence to suggest that the number of resistant isolates was increasing.
Gram-negative bacilli are a common cause of infections in hospitalized cancer patients. Consequently, the discovery of new antibiotics with activity against these organisms are of major importance. Cephalosporins have proven to be significantly active against Klebsiella pneumoniae, Escherichia coli, Proteus mirabilis and most gram-positive cocci.1) Since the introduction of cephalothin, numerous derivatives have been synthesized which offer advantages such as oral administration, less toxicity and higher and more prolonged serum concentrations. This study was initiated to evaluate the comparative in vitro activity of the cephalosporins against gram-negative bacilli and gram-positive cocci and to determine whether the increased use of these antibiotics had resulted in the emergence of increasing numbers of resistant organisms. Materials and Methods Susceptible testing was conducted on 443 isolates of gram-negative bacilli and gram-positive cocci using a dilution technique with an automatic microtiter system.2.3) The organisms were inoculated into MUELLER-HINTON broth (Difco) and incubated at 37°C for 18 hours. A 0.05-ml sample of 10-3 dilution of the broth cultures of gram-negative bacilli and Staphylococcusaureus (approximately 106 colony forming units/ml) was used as the inoculum for the susceptibility tests. A 0.05-ml sample of a 10-2 dilution of the broth cultures of Diplococcus pneumoniae and Streptococcus pyogenes (approximately 106 colony forming units/ml) was used as the inoculum. All gram-negative bacilli were isolated from blood specimens of patients between 1967 and 1973. The majority of these patients were hospitalized at this institution and had underlying malignancies. A total of 160 isolates of K. pneumoniae, 130 isolates of E. coli and 88 isolates of P. mirabilis were tested. Supported Health,
in part
U. S. Public
by
Grant
Health
CA Service,
10042 from Bethesda,
the
National
Maryland
Cancer 20014.
Institute,
National
Institutes
of
THE
182
JOURNAL
OF
ANTIBIOTICS
FEB.
1976
All gram-positive cocci were obtained from hospitalized patients, some of whom did not have cancer. A total of 15 isolates of Diplococcus pneumoniae and 50 isolates of Staphylococcus aureus were studied. Isolates of S. aureus were tested according to their susceptibility to penicillin G. Those 25 organisms inhibited by less than 0.10 µg/ml were considered to be penicillin G susceptible and those 25 organisms resistant to more than 25µg/ml were considered to be penicillin G resistant. µg The antibiotics, cephalothin, cephalexin and cephaloridine were supplied by Eli Lilly and Co., Indianapolis, Indiana. Merck, Sharp & Dohme supplied cephamycin C and cefoxitin. Cephradine, cephapirin, cefazolin and cephacetrile were obtained from the following companies, respectively: E. R. Squibb & Sons, Inc., Princeton, N. Y.; Bristol Laboratories, Syracuse, New York; Smith Kline & French, Philadelphia, Penn. and CIBA Pharmaceutical Co., Summit, N.J. Initial concentrations of 1,000µg/ml were prepared and appropriate dilutions from this stock concentration were made. Fig. 1. Activity of cephalosporins cherichia coli (130 isolates tested).
Results
At a concentration the
cephalosporins
cephapirin
of
12.5 µg/ml,
except
inhibited
over
At
only
the same
losporins
6%
inhibited
of K. pneumoniae 90%,
but
Cefoxitin,
(Fig. 3). cephalexin,
Fig.
2.
the
inhibited
isolates inhibited
only
and cefazolin
cephalosporins
Activity spp.
of
Cefoxitin
against
Cephalexin Cephaloridine Cephalothin Cephapirin Cefoxitin Cephamycin C Cephradine Cephacetrile Cefazolin
65%.
were
the
P. mirabilis
At a concentration of 12.5 µg/ml, cephaloridine, cephalothin, cepha-
cephamycin
siella
respectively.
all of the cepha-
over 60%
cephapirin
of
and cephalothin
38 %,
(Fig. 2).
cephalothin
most active
pirin,
and
concentration,
Es-
and
60 % of the isolates
of E. coli (Fig. 1). Cephapirin inhibited
all
cephalothin
against
C and
cefazolin
of cephalosporins
(160 isolates Cephalexin Cephaloridine Cephalothin Cephapirin Celoxitin Cephamycin C Cephradine Cephacetrile Cefazolin
tested).
inhibited
against
Kleb-
Fig. 3. Activity of cephalosporins mirabilis (88 isolates tested). Cepholexin Cephaloridine Cephalothin Cephapirin Cefoxitin Cephamycin C Cephradine Cephacetrile Cefazolin
against Proteus
VOL.
XXIX Fig.
NO.
2
4.
THE
Activity
JOURNAL
of cephalosporins
against
OF
183
ANTIBIOTICS
penicillin
G resistant
Staphylococcus
o-o-
Fig.
5.
Activity
of cephalosporins
against
penicillin
Cepholexin Cephaloridine Cephalolhin
~-
Cephopirin
o-•-•-
Cefoxitin Cephomycin Cephrodine Cephocetrile
o--
Cefozolin
G sensitive
aureus.
C
Staphylococcus
aureus.
Cephalexin Cephaloridine Cephalothin Cephapirin Cefoxitin Cephamycin C Cephradine Cephacetrile Cefazolin
more
than
90 % of these isolates.
Cefoxitin inhibited
was consistently
87 % of isolates
6.25 µg/ml, There
it inhibited were
intermediate mycin
cephalosporin
differences
of
of K. pneumoniae in the
against
in vitro
and cefoxitin, against
both
cephalexin
penicillin
gram-negative
12.5µg/ml. and
activity
and resistant S. aureus (Figs. 4 and 5). of S. aureus. Cephalothin, cefazolin,
in activity,
C was inactive
active
of E. coli at a concentration
84 % of isolates
substantial
penicillin G sensitive against both groups
the most
At
the
and resistant
It of
of P. mirabilis.
cephalosporins
Cephaloridine cephacetrile
and cephradine
G sensitive
a concentration
100 % of isolates of
bacilli.
against
was the most active and cephapirin were
were
least active.
S. aureus.
There
Cephawere
VOL.
XXIX
inhibited
from
THE
1 lists the proportion
cephalosporin
substantially during
2
JOURNAL
only 47 % at a concentration
Table of each
NO.
by year.
from year to year.
this period.
to 92 j.
Some
in susceptibility statistically
of
significant
of E. coli and
The susceptibility Cephalothin
of these
of isolates
are statistically
Likewise,
the
bacilli
most extensively
significant. and
differences cephapirin
to 12.5 µg/ml has fluctuated
at this institution
to this antibiotic
K. pneumoniae
in 1968
pneumoniae to cephalothin, cephalexin, cephaloridine, to 1968 are statistically significant (p=.001~.007).
sensitive
gram-negative
of E. coli susceptible
of susceptible
of E. coli to cephalothin
(p=.003).
185
K. pneumoniae
has been used
the proportion
these differences
of isolates
ANTIBIOTICS
of 6.25 µg/ml.
of isolates
The proportion
16 % to 64 % whereas
OF
For example, 1973
has varied
has varied
and cefazolin
44%
the differences
compared
in susceptibility
from
to
1971 are
of isolates
of K.
in 1970 compared
Discussion This in vitro data indicates that the cephalosporin antibiotics have a broad spectrum of activity against gram-negative bacilli and gram-positive cocci. Cefoxitin was the most active antibiotic against isolates of gram-negative bacilli. WALLICK and HENDLIN found similar results with their susceptibility testing of cefoxitin.4) Cefazolin inhibited 78 % of the Klebsiella spp. isolates at a concentration of 6.25 µg/ml. TURCK et al. found similar results with cefazolin. In their study, more than 80% of isolates were inhibited by a concentration of 5 µg/ml or less.5) Cephapirin exhibited the least activity against isolates of E. coli and Klebsiella spp. whereas cephradine was least active against P. mirabilis. S. aureus isolates were most sensitive to cephaloridine and cephalothin, and the results were similar regardless of their susceptibility to penicillin G. Other investigators found that cefazolin was equally active against penicillin G sensitive and resistant S. aureus.5) However, in this study, cefazolin was less active against penicillin G resistant isolates of S. aureus. At a concentration of 0.20µg/ml, cefazolin inhibited 68 % of penicillin G sensitive isolates, but only 24% of penicillin G resistant isolates. Cefoxitin, cephalexin and cephradine were the least active cephalosporins against gram-positive cocci, except for cephamycin C which was inactive against S. aureus and only marginally active against D. pneumoniae. In NEU'S study, cefoxitin had similar activity as cephalexin.6) In the study of BERGERON et al., cefazolin and cephaloridine were more active than cephalothin and cephalexin against D. pneumoniae.7) However, cephaloridine is not as consistently active as cephalothin when a high inoculum of S. aureus is used. The susceptibility of isolates of E. coli and K. pneumoniae to the cephalosporins has fluctuated substantially during the years from 1968 to 1973. Some of the most striking differences were observed with isolates of K. pneumoniae, comparing 1968 with 1970, differences which were statistically significant. It was not possible to correlate the dramatic decrease in cephalosporin susceptibility in 1970 to any change in antibiotic usage in this institution. Fortunately, since that time, the number of cephalosporin resistant isolates has decreased, although cephalothin usage was not altered. An explanation for this fluctuation in susceptibility is not readily apparent. Cefoxitin susceptibility fluctuated the least and it was the most active of the cephalosporins. This cephalosporin is resistant to hydrolysis by gram-negative bacilli. Some of the variability in the sensitivity of E. coli to cephalosporins may be due to the fact that E. coli vary in their ability to produce ß-lactamases which results in their resistance. Another factor which may play a role is the degree of cell permeability to the antibiotics. Although K. pneumoniae seldom produce cephalosporinases, it is possible that the production of cephalosporinases may explain the changing susceptibility of these organisms to cephalothin.1)' In vitro evaluation of the cephalosporins has indicated that they have substantial differences in activity against gram-positive cocci and gram-negative bacilli. Consequently, use of a single
VOL.
XXIX
inhibited
from
THE
1 lists the proportion
cephalosporin
substantially during
2
JOURNAL
only 47 % at a concentration
Table of each
NO.
by year.
from year to year.
this period.
to 92 j.
Some
in susceptibility statistically
of
significant
of E. coli and
The susceptibility Cephalothin
of these
of isolates
are statistically
Likewise,
the
bacilli
most extensively
significant. and
differences cephapirin
to 12.5 µg/ml has fluctuated
at this institution
to this antibiotic
K. pneumoniae
in 1968
pneumoniae to cephalothin, cephalexin, cephaloridine, to 1968 are statistically significant (p=.001~.007).
sensitive
gram-negative
of E. coli susceptible
of susceptible
of E. coli to cephalothin
(p=.003).
185
K. pneumoniae
has been used
the proportion
these differences
of isolates
ANTIBIOTICS
of 6.25 µg/ml.
of isolates
The proportion
16 % to 64 % whereas
OF
For example, 1973
has varied
has varied
and cefazolin
44%
the differences
compared
in susceptibility
from
to
1971 are
of isolates
of K.
in 1970 compared
Discussion This in vitro data indicates that the cephalosporin antibiotics have a broad spectrum of activity against gram-negative bacilli and gram-positive cocci. Cefoxitin was the most active antibiotic against isolates of gram-negative bacilli. WALLICK and HENDLIN found similar results with their susceptibility testing of cefoxitin.4) Cefazolin inhibited 78 % of the Klebsiella spp. isolates at a concentration of 6.25 µg/ml. TURCK et al. found similar results with cefazolin. In their study, more than 80% of isolates were inhibited by a concentration of 5 µg/ml or less.5) Cephapirin exhibited the least activity against isolates of E. coli and Klebsiella spp. whereas cephradine was least active against P. mirabilis. S. aureus isolates were most sensitive to cephaloridine and cephalothin, and the results were similar regardless of their susceptibility to penicillin G. Other investigators found that cefazolin was equally active against penicillin G sensitive and resistant S. aureus.5) However, in this study, cefazolin was less active against penicillin G resistant isolates of S. aureus. At a concentration of 0.20µg/ml, cefazolin inhibited 68 % of penicillin G sensitive isolates, but only 24% of penicillin G resistant isolates. Cefoxitin, cephalexin and cephradine were the least active cephalosporins against gram-positive cocci, except for cephamycin C which was inactive against S. aureus and only marginally active against D. pneumoniae. In NEU'S study, cefoxitin had similar activity as cephalexin.6) In the study of BERGERON et al., cefazolin and cephaloridine were more active than cephalothin and cephalexin against D. pneumoniae.7) However, cephaloridine is not as consistently active as cephalothin when a high inoculum of S. aureus is used. The susceptibility of isolates of E. coli and K. pneumoniae to the cephalosporins has fluctuated substantially during the years from 1968 to 1973. Some of the most striking differences were observed with isolates of K. pneumoniae, comparing 1968 with 1970, differences which were statistically significant. It was not possible to correlate the dramatic decrease in cephalosporin susceptibility in 1970 to any change in antibiotic usage in this institution. Fortunately, since that time, the number of cephalosporin resistant isolates has decreased, although cephalothin usage was not altered. An explanation for this fluctuation in susceptibility is not readily apparent. Cefoxitin susceptibility fluctuated the least and it was the most active of the cephalosporins. This cephalosporin is resistant to hydrolysis by gram-negative bacilli. Some of the variability in the sensitivity of E. coli to cephalosporins may be due to the fact that E. coli vary in their ability to produce ß-lactamases which results in their resistance. Another factor which may play a role is the degree of cell permeability to the antibiotics. Although K. pneumoniae seldom produce cephalosporinases, it is possible that the production of cephalosporinases may explain the changing susceptibility of these organisms to cephalothin.1)' In vitro evaluation of the cephalosporins has indicated that they have substantial differences in activity against gram-positive cocci and gram-negative bacilli. Consequently, use of a single
186
THE
JOURNAL
cephalosporin for routine in vitro susceptibility tion of the appropriate cephalosporin as therapy
OF
ANTIBIOTICS
FEB.
1976
testing is probably inadequate. However, selecalso depends on other factors such as their relative
potential for causing thrombophlebitis and nephrotoxicity and which may offer the advantage of higher serum concentrations
their pharmacological disposition or better tissue penetration.
References
1) HEWITT, W.L.: Cephalosporins-1973. J. Infect. Dis. 128 Supplement, October 1973 2) Canalco: Autotiter IV Instruction Manual 3) STEWART, D. & G.P. BODEY: In vitro activity of sisomicin, an aminoglycoside antibiotic against clinical isolates. J. Antibiotics 28: 149~155, 1975 4) WALLICK, H. & D. HENDLIN: Cefoxitin, a semisynthetic cephamycin antibiotic: Susceptibility studies. Antimicr. Agents & Chemoth. 5: 25~32, 1974 5) TURCK, M.; R. A. CLARK, H. W. BEATY, K. K. HOLMES, W. W. KARNEY & L. B. RELLER: Cefazolin in the treatment of bacterial pneumonia. J. Infect. Dis. 128: S382~385, 1973 6) NEU, H. C.: Cefoxitin, a semisynthetic cephamycin antibiotic: Antibacterial spectrum and resistance to hydrolysis by gram-negative beta-lactamases. Antimicr. Agents & Chemoth. 6: 170~176, 1974 7) BERGERON, M. C.; J. L. BRUSCH, M. BARZA & L. WEINSTEIN: Bactericidal activity and pharmacology of cefazolin. Antimicr. Agents & Chemoth. 4: 396~401, 1973
